Identification devices comprise a wide variety of products such as, for example, marker sleeves, tags, labels and nameplates, that are intended to be applied to an article in order to provide specific identification of the article. Electrical wires, pipes and other conduits, and panels, are but a few examples of the many types of articles that often need to be identified in this fashion. In many instances, the end user of the identification device, typically the manufacturer of the product to be identified, must be able to print alpha-numeric indicia on the identification device in order to precisely identify a particular article. For example, aircraft manufacturers apply sleeves bearing a serial number to identify a specific wire, or tags to identify a specific bundle of wires, or labels or sleeves to identify a particular pipe in a hydraulic system. This requirement imposes a need for identification devices to which a user can apply identification data by printing systems typically available in plants and offices, such as with a computer printer, typewriter, or manually with a writing pen.
Various identification devices are made with plastic substrates, such as a sheet of plastic film for a marker sleeve or tag, and others are made with metallic substrates such as aluminum foil or metal plates. Many of these materials commonly used as substrates for indentification devices cannot be printed by means of the equipment noted above, such as computer printers and typewriters, and it is therefore necessary to apply a coating to the substrate that is capable of receiving and retaining printed indicia. Various types of printable coatings are known in the art that are satisfactory for use as coatings for identification devices that are to be subjected to relatively mild ambient conditions.
However, a special need has developed for identification devices that are capable of withstanding exposure to rigorous conditions, particularly with respect to temperature and solvents. This in turn has resulted in a need to develop printable coatings that can be used to receive and retain printing for such highperformance identification devices. Most printable coatings involve at least two essential elements, a filmforming polymer and inorganic solid particulates that are mixed with the film-forming polymer in order to impart ink receptivity and retention. One of the prior art coatings used for high-performance indentification devices is made with a polyimide film-forming polymer and solid particulate materials such as magnesium silicate, calcium carbonate and the like. The coating is applied to, for example, plastic substrates capable of withstanding high temperatures such as Teflon (Reg. Trademark) and similar materials. However, identification devices made with this prior art coating have at least two disadvantages which preclude their application to especially rigorous conditions: unsatisfactory resistance to very strong solvent fluids such as some hydraulic fluids and rather low flexibility so that the coatings will tend to crack when employed with an identification device that is placed about a round article, for example.
One of the principal objects of this invention was to develop a high-performance printable coating that can be used to produce an identification device that can withstand high temperatures and strong solvents. Another principal object was to develop a printable coating meeting the foregoing criteria which can also be formulated to provide a very flexible coating. A further main object was to develop identification devices employing substrates capable of withstanding relatively high temperatures and bearing a printable coating meeting the foregoing objectives.